1. Field of the Invention
The present invention relates to a lens barrel, and in particular, to the construction for miniaturizing a zoom lens barrel having a lens barrel capable of advancing and retreating.
2. Related Art Statement
In a zoom lens barrel in which a plurality of lens groups including a focus lens group is made to move in the direction of an optical axis and to perform zoom operation, cam grooves for driving different lens groups that separately advance and retreat respectively are separately formed according to respective movements.
In addition, in such a lens barrel, advance of the focus lens group is performed using the infinite position as a datum, and in case of focusing in the vicinity, focusing is performed by advancing the focus lens group from the infinite position to a closeup position.
FIGS. 12A, 12B, and 12C show a zoom lens whose phototaking lens is composed of three groups of lenses, and show an example of a tube-retraction type of zoom lens barrel in which the second lens group is a focus lens. FIG. 12A is an explanatory diagram showing positions of respective lens groups in a tube retracting state. FIG. 12B is an explanatory diagram showing positions of respective lens groups in a wide-angle state. FIG. 12C is an explanatory diagram showing positions of respective lens groups in a telescopic state.
As shown in FIGS. 12B and 12C, when the zoom lens barrel is in the wide-angle state and telescopic state, the second lens group (focus lens group) 202 is usually positioned at the infinite position shown by solid lines in the figure against the first and third lens group 201 and 203. In addition, focusing to the vicinity is performed by advancing the second lens group 202 from the infinite position to the closeup position in the first lens group side that is shown by alternate long and two short dashes lines. After photo-taking, the second lens group 202 is moved to the infinite position by being reset.
Furthermore, a method for containing this zoom lens barrel at a tube retracting position after photo-taking is as follows. As shown in FIG. 12A, the second lens group 202 is not moved from the infinite position, that is, the second lens group 202 keeps the state being reset at the infinite position. On the other hand, with keeping the distance between the first lens group 201 and second lens group 202 and moving them as one piece, the entire length of the lens barrel is shortened and the lens barrel is contained by shortening a zoom distance between the first lens group 201 and third lens group 203. Therefore, when the tube retraction is completed space remains for closeup feeding length of the focus lens group.
In conventional cam grooves for movement of lens groups, it is difficult to sufficiently secure movable ranges of respective lens groups because a plurality of cam grooves are provided on the same circumferential surface of the same cam tube.
Thus, if a plurality of different cam grooves are formed adjacent to each other, rotation angles of the cam grooves become small, and thus increase the pressure on each cam groove when the cam tube rotates. If the diameter of the cam tube is made to be large so as to reduce this pressure, the lens barrel becomes correspondingly large. In addition, if cam grooves are formed shifted to the thrust direction lest respective cam grooves should overlap without the cam grooves being adjacent to each other, the entire length of the cam tube becomes large. Hence, the lens barrel also becomes large in this case.
In this manner, using respective cam grooves separately causes a malfunction that the entire size of the lens barrel becomes large in radial directions or in the thrust direction.
Furthermore, as described above, when the zoom lens barrel is retracted, a surplus space for closeup feeding length of the focus lens group is kept in the front of the focus lens group. As a consequence, the entire length of the lens barrel at the tube retraction becomes large.
Moreover, in a lens barrel shown in FIGS. 12A to 12C, if a cam for tube retraction is provided by extending a zoom cam moving the first lens group 201 for zooming so as to shorten the distance between the first lens group 201 and second lens group 202 for the sake of reducing the entire length of the lens barrel, this causes additional difficulty of cam layout in the cam tube and enlargement of the cam tube.
In addition, since the first lens group 201 that is a zoom lens is moved so as to shorten the distance between the first lens group 201 and second lens group 202, the load for electrically driving the cam tube becomes large.